1. Field
Embodiments of the present invention relate to a sensor unit having a simple sensor structure to detect intensity of force applied to a parking cable upon braking a vehicle and an electronic parking brake with the same.
2. Description of the Related Art
Generally, an electronic parking brake (EPB) is a parking brake in which driving of the parking brake is electronically controlled. That is, the EPB applies brake force to wheels of a vehicle in an electronically controlled manner, to prevent the wheels from rotating.
Such an EPB includes a force sensor to sense tension exerted on a parking cable and displacement of the parking cable. The force sensor includes a magnet and a Hall IC. The Hall IC senses variation of electric field generated by the magnet, and outputs a sensing signal.
FIG. 1 is a sectional view illustrating a coupled state of a power conversion unit 10 and a force sensor 20 in a conventional electronic parking brake.
Referring to FIG. 1, the force sensor 20 is mounted to the power conversion unit 10, which converts rotation into rectilinear motion, in order to measure intensity of force exerted on a parking cable C.
The power conversion unit 10 is connected to a reduction gear unit (not shown) to reduce rotation speed of a motor (not shown), in order to convert rotation of the motor into a rectilinear motion. The power conversion unit 10 includes a screw member 11 connected, at one end thereof, with the parking cable C, a nut member 12 to move along an axial direction of the screw member 11 relative to the screw member 11, and a gear member 13 coupled to an outer peripheral surface of the nut member 12, to rotate together with the nut member 12.
The nut member 12 has a hollow structure having an axial hole. The screw member 11 is threadedly coupled to the axial hole of the nut member 12 at one end of the nut member 12, to move relative to the nut member 12 in accordance with rotation of the nut member 12, and thus to actuate the parking cable C. The force sensor 20 is mounted to the other end of the nut member 12, to measure brake force exerted on the parking cable C.
As shown in FIG. 2, the force sensor 20 includes a sensor housing 21, in which a Hall IC 22 to sense variation of magnetic force caused by displacement of a magnet 24, a latch 26 fixed to one side of the sensor housing 21, and a magnet housing 23 disposed within the sensor housing 21. The magnet 24 is installed in the magnet housing 23. The force sensor 20 also includes an elastic member 25 to elastically support the sensor housing 21 between the magnet housing 23 and the sensor housing 21.
The magnet housing 23 has a portion extending outwardly of the sensor housing 21 through the other side of the sensor housing 21. The extension portion of the magnet housing 23 functions to mount the magnet housing 23. That is, the portion of the magnet housing 23 exposed outwardly of the sensor housing 21 is mounted to a housing (not shown), which forms an outer appearance of the electronic parking brake, by a housing support 27.
The latch 26 is mounted to the sensor housing 21 such that a portion of the latch 26 is protruded outwardly of the sensor housing 21 through one side of the sensor housing 21. The latch 26 is connected to the other end of the nut member 12 by a bearing module 30. Thus, the sensor housing 21 is moved by the latch 26 in accordance with movement of the nut member 12.
The bearing module 30 includes a connecting shaft 32 connected to the nut member 12, a bearing 33 fitted around the connecting shaft 32, and a bearing housing 31 to enclose the latch 26 as well as the bearing 33.
The bearing housing 31 holds the portion of the latch 26 protruded from the sensor housing 21. Thus, when the nut member 12 moves relative to the screw member 11, the sensor housing 21 is moved together with the latch 26 because the rotation and axial displacement of the nut member 12 are converted into rectilinear motion by the bearing 33. In accordance with movement of the latch 26, the sensor housing 21 is moved. However, the magnet housing 23 is prevented from moving by the housing support 27. Accordingly, relative displacement is generated between the magnet 24 and the Hall IC 22. The force sensor 20 detects intensity of force exerted on the parking cable C, based on the relative displacement between the magnet 24 and the Hall IC 22.
In the above-mentioned force sensor 20, however, the bearing module 30 is installed between the power conversion unit 10 and the force sensor 20, to convert rotation into rectilinear motion for movement of the sensor housing 21, in order to measure intensity of force exerted on the parking cable C. In this regard, the force sensor 20 requires a complex assembly structure for measurement of the braking force of the parking cable C.
Furthermore, the structure of the force sensor 20 and the structure of the electronic parking brake become more complex due to the structure of the latch 26 installed to connect the bearing module 30 and force sensor 20 and the structure of the housing support 27 separately provided to maintain the magnet housing 23 in a fixed state for displacement measurement of the force sensor 20. As a result, the number of elements to be assembled is increased, and the number of assembly processes is increased.